Line of Operation

(The) in war. The line between the base of operation (q.v.) and the object aimed at. Thus, if a fleet is the base and the siege of
a city is the object aimed at, the line of operation is that drawn from
the fleet to the city. If a well-fortified spot is the base and a
battle the object, the line of operation is that which lies between the
fortified spot and the battle-field.